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<a name="boost.proto.context.callable_context.eval"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct template eval</span></h2>
<p>boost::proto::context::callable_context::eval</p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../../proto/reference.html#header.boost.proto.context.callable_hpp" title="Header &lt;boost/proto/context/callable.hpp&gt;">boost/proto/context/callable.hpp</a>&gt;

</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> ThisContext <span class="special">=</span> <span class="identifier">Context</span><span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="eval.html" title="Struct template eval">eval</a> <span class="special">:</span> <span class="keyword"></span> <em class="replaceable"><code>see-below</code></em> <span class="special">{</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp145212832"></a><h2>Description</h2>
<p>
                A BinaryFunction that accepts an <code class="computeroutput">Expr</code> and a
                <code class="computeroutput">Context</code>, and either fans out the expression and passes
                it to the context, or else hands off the expression to <code class="computeroutput">DefaultCtx</code>.
              </p>
<p>
                If <code class="computeroutput">Context</code> is a <a class="link" href="../../../../PolymorphicFunctionObject.html" title="Concept PolymorphicFunctionObject">PolymorphicFunctionObject</a>
                such that it can be invoked with the tag and children of <code class="computeroutput">Expr</code>, as
                <code class="computeroutput">ctx(typename Expr::proto_tag(), child_c&lt;0&gt;(expr),... child_c&lt;N&gt;(expr))</code>,
                then <code class="computeroutput">eval&lt;Expr, ThisContext&gt;</code> inherits from
                <code class="computeroutput"><a class="link" href="../callable_eval.html" title="Struct template callable_eval">proto::context::callable_eval</a>&lt;Expr, ThisContext&gt;</code>.
                Otherwise, <code class="computeroutput">eval&lt;Expr, ThisContext&gt;</code> inherits from
                <code class="computeroutput">DefaultCtx::eval&lt;Expr, Context&gt;</code>.
              </p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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